1. Field of the Invention
The present invention relates to semiconductor wafer processing and, more particularly, to desorption of one or more contaminants from a surface of a semiconductor wafer.
2. Description of Related Art
Semiconductor substrates, especially silicon wafers, can form a layer of surface contamination. This surface contamination is undesirable because it can adversely affect wafer processing and monitoring. This contamination comes from the local untreated atmosphere, which is typically a mixture of numerous gases and gaseous vapors. It is believed that these gases and vapors condensate on the surface of the wafer forming a liquid or semi-liquid film. Although the constituents of this contamination layer are not precisely known, it is believed that water is a primary component. The other contaminants are comprised mostly of various hydrocarbon molecules, which are collectively referred as organics.
One approach to removing the contamination layer is heating the wafer. Heretofore, heating a wafer has been accomplished by radiation or conduction. One radiation heating technique includes placing a wafer under a heating element and heating the topside of the wafer primarily through radiation. Practical radiation heating requires holding the heat source at temperatures significantly higher than the desired surface temperature. This heat can create undesirable temperature increases in the surrounding area which would necessitate additional thermal management techniques.
Since it is directly over the top surface of a wafer, a radiation heating element must be sealed and non-contaminating even at high temperatures. Sealing the element can reduce radiation effectiveness requiring even a higher temperature heat source. Materials that meet the non-contaminating requirements can also be expensive and hard to manufacture. An array of linear heating elements can create cool zones between the elements resulting in uneven heating of the wafer surface.
One conduction heating technique includes placing the wafer onto a heated surface, such as a hotplate. The wafer is then heated primarily through conduction from the backside of the wafer until the topside has reached a desired temperature. One problem with using a heating plate results from the use of robotic arms that transport the wafer by the backside thereof. Setting the wafer down onto the heated surface of the hotplate requires withdrawing of the robotic arm. A mechanical wafer lowering mechanism or a recessed pocket in the surface of the hotplate is usually required to accomplish this. A wafer lowering mechanism adds system complexity while a recessed pocket can create uneven wafer heating. Another problem with conduction heating is a possibility of contaminating the backside of the wafer by the hotplate itself.
It would, therefore, be desirable to provide an apparatus and method that avoids the foregoing problems, and others, while enabling the temperature of a semiconductor wafer to be raised sufficiently to facilitate desorption of contaminants thereon for subsequent testing thereof.